Device for measuring fluid pressures



Feb-24, 1942. J. F.`INDERDOHNEN E-r A1. 2,274,479

DEVICE FOR MEASRING FLUID PRESSUHES Filed July 22, '1959 2 Sheets-Sheet l ATTORNEY. V

Feb., 24, 1.942. J. F. |NDERDOHNEN E-r AL.. 2,274,479

DEVICE FOR MEASURING FLUID PRESSURES Filed July 22, 1939 2 Sheets-Sheet 2 Patented Feb. 24, 1942 i DEVCE FOR MEASURING FLUID PRESSURES John F.

Index-dehnen, Milwaukee, Wis., and Alphonso Noble, Naugatuck, Conn., assignors to The Bristol Company, corporation of Connecticut v Application July 22, 1939, Serial No. 285,852 9 claims. (C1. vs -31') This invention relates to devices for measuring fluid'pressures, and more especially to means for isolating a measured iiuid from a measuring instrument when suchfluid may be either of a cor-v rosive nature, or subject to contamination, or otherwise unsuited to direct contact with interior parts of an instrument, and is particularly adapted to such use when the pressures involved vmay be of relatively high values.

In the measurement of properties of corrosive fluids, there are many instances where a suitable measuring unit cannot be designed to withstand the action of such fluids in its delicate interior parts, whereas a relatively simple 'tubular structure may be constructed of a material not subject to damage by said fluids. Again, in the measurement of uids containing solid matter in suspension or such objects as chips, as in the cult, if not impossible, to clean and sterilize and maintain in a sanitary condition.

It is an object of this invention to provide a pressure-sensitive element yadapted for the transmission of fluid pressures to a measuring unit, while maintaining complete isolation between the measured fluid and the interior parts of the unit.

It is a further object of the invention to provide a device of the above nature which shall be free of pockets or crevices matter 'may accumulate.

A still further object of the invention is to provide means whereby changes in the temperature of the fluid under treatment, or of the ambient l case of a sulphite digester, these materials have wherein undesirable temperature, may be compensated for, and rendered ineffective in the ultimate measurement.

Another object is to provide a device of the above nature which shall have an inherent tend- V encyto damp out rapid-fluctuations in the measured pressure withoutthe need for constricted passages carrying the fluid under measurement.

Still another object' is to provide a deviceof the above nature which shall be simple and Vspond only in tension,

Waterbury, Conn., a

rugged in construction, readily dis-assembled for cleaning, and capable of manufacture at a reasonable cost.

For this purpose it is proposed to provide a pressure-sensitive fitting including a smoothbored tubular part having a deformable elastic wall, and adapted to carry a continuous stream of the liuid whose pressure is to be measured, said tubular part being enclosed within a nondeformable body part and separated therefrom by an annular chamber of variable volume adapted to contain an incompressible fluid through the medium of which deformations vof said wall due to pressure fluidmay be measured ina pressuresensitive instrument, y

In the use of a tubular element deformable in response to internal fluid pressure, utilization may be made of either of two' mechanical principles, the one involving a tubular element of normally non-'circular cross-section and the other an element of normally circular section. It will be appreciated that the mechanisms of response of these two forms are essentially different. Thus, the tube of non-circular section under the influence of internal pressure will tend to assume a section having maximum internal area without change in periphery, which, of course, is a circle; and the principal stresses set up in its walls will be in the nature of bending stresses. The circular tube, on the other hand, can reing under the applied internal pressure, with a corresponding increase in' circumference. In either application, it is proposed to position the deformable tubular element within a chamber having non-deformable outer walls, so that the increase in cross-section area due to the approach of the non-circular tube to a circular section or to the increase in circumference of the circular tube, will produce a resultant reduction on section area of the surrounding annular space,

with a corresponding reduction in volume of the chamber formed thereby, causing contained i liquid to be forced out 'of the chamber. v

It is further proposed to provide within said body part a chamber ofconstantvolume, thermally associated with the variable volume chamber, and adapted to contain a liquid whereby may be obtained compensation for changes in the temperature of the liquid in the latter.

The nature of the invention, however, will best be understood when described in connection with the accompanying drawings, in which:

Fig. 1 is a front elevation, partly in vertical of said first-named the wall actually stretchadapted to yield in ment I 4 and -ber 2|.

section, of a compound, internal-pressure-sensitive fitting with measuring instrument and embodying the principles of the invention.

- shown in the drawings.

Fig. 2 shows a transverse sectional view of the' fitting taken von the line 2-2, Fig. 1 of the drawings and lookin-g in the direction vof the arrows.

Fig. 3 is a fragmentary vertical section, on an enlarged scale, showingcertain structural details of the tting. j

Fig. 4 is a front elevation, partly in.vertical section, of an alternative form of fitting embodying the principles of the invention.

Fig. 5 is a transverse sectional view of the same taken on the line 5 5, Fig. 4 of the drawings, and looking in the direction of the arrows; and

Fig. 6 is a similar view showing an alternative form which may be normally assumed by the internal parts.

Figs. 7 and 8 are fragmentary vertical and horizontal sections, respectively, of an alternative form which'may be taken by of the fitting.

Fig. 9 is a diagrammatic view of two elements embodying the invention, applied tov the measurement of uid now in a closed conduit.

Referring to the drawings, more particularly Figs. l to 3 thereof, I0 designates an elongated cylindrical elements'formed from a section of straight elastic metal tubing having end portions or flanges II- and I2 left full size, the intermediate portion being reduced to form a thin wall a tensile sense to internal uid pressure, but not to acquire a permanent setvunder-pressures of the order of those to be measured. Surrounding the element I is a similar tubular element I4 of an inside diameter the same as the outside diameter of the end portions II .and I2, and'. having end portions or anges I and I6 left full size, the intermediate portion being reduced, but not su'iciently to weaken materially the tube wall. Surrounding the element I4 is a tubular element .I8 having an'inside diameter the same as the outside diam-Q eter of the end portions I5 and I6,"and its outside diameter uniform throughout its length.

A massive elongated metallic body part I9 has axially formed therethrough a cylindrical bore of diameter equal to the outside diameter of the tubular element I8, and adapted to contain and support the same together with the elements I4 and I0 when the latter are coaxially positioned therein.

Thus, with said tubular elements so positioned,

annular chamber between the outer surface of element' I0 and the inner surface of element I4, and another and coaxially disposed annular chamber 2| between the outer surface of elethe inner surface of element I8, the tubular element Ill constituting a conduit adapted to carry a flowing fluid Whose static pressurewilll be exerted against the yieldable walls of said element. Y

Through an aperture drilled in the end portion of element I9 is fitted a capillary tube A22 communicating with the chamber 20; and similarly a capillary tube 23 communicates with the cham- The capillary tubes 22 and 23 are bent substantially at right angles and are carried through a lateral opening-24 formed in the body part I9. The outer end of said opening is threaded to receive a plug or nipple 25, serving partial cloand for the mounting of certain elements The assembly of the coaxial tubular elements and connecting capillary tubing being positioned within the body part I9 as-shown in Fig. 1, the extremities of the tubular elements are sealed to each other by brazing or soldering, and to the body part by means of fillets of solder or thermoplastic or synthetic resin material or the like. This material is allowed to flow into the opening 24, securing the capillary tubes therein and retaining the plug or into smooth flares 26 and 21, presenting no sharp corners or interstices subject to the accumulation of deposits or diiiicult to clean when the tting is disassembled.

The body part I9 is formed with seats 28 and 29 on its respective ends, whereby connection may be made with union parts 30'and 3|, forming elements in the piping system wherein pressures are to be determined; and the end portions are externally threaded to be engaged by suit able clamping rings 32 and 33, forcing said union parts into' fluid-tight engagement with the seated ends of the body part I9, the whole constituting an annular, internal-fluid-pressure-sensitive device including a conduit part adapted to form a section' in the piping system, and being readily removable therefrom for inspection and cleaning. The novel tting, moreover, presents no objectionable obstructions, recesses, or interstices when assembled for use.

A pressure gauge suitable to use in conjunction with the apparatus hereinabove set forth may take the following form:

Upon a base 35 is mounted a' Bourdon tube 36,

adapted to have its free end deflected in a counclockwise sense relative to ter-clockwise sense upon the pressure within the tube. Carried by the free end of said Bourdon tube is another Bourdon tube 31, adapted for deection in an opposite or its point of support upon the application of internal pressure. Carried by the free endof the Bourdon tube 31 is an index or pointer 38-adapted to be deflected thereby, and to provide by its deflection, relative to a graduated scale 39 mounted on the base 35, a measure of the deflection of the free end of the Bourdon tube 31 with respect to the base of the application of fluid instrument. The interior space of the Bourdon uids and in respect to which the tube 36 is placed in communication with the annular chamber ZI lby means of the capillary tube 23 and the interior space of the tube 31 with the chamber 20 through a flexible section 40 forming a part of the capillary tube 22. Thus there are provided two closed, adjacent, but non-communicating, systems adaptedto contain fluid or index or pointer 38 will respond diierentially to similar changes in uid pressure within said systems. The interior spaces of the systems are completely lled with an incompressible liquid such as kerosene, and sealed. The apparatus may thus be made inherently self-compensating for changes 'in volume of the contained liquidsdue to variations in temperature. For example, because of the intimate thermal association of the chambers 20 and 2|, being separated only by the metallic wall I4, the liquids contained in these spaces will at all times attain substantially equal temperanipple 25 in its thread, and is l V formed at each extremity of the tubular elements perature will cause some of springs being properly proportioned, the 'deflection of the Bourdon spring 36 may be caused exactly to neutralize that of spring 31, so that changes in' temperature of the actuating liquids or of the parts with which they come in contactv will have no eiectupon the ultimate indication of the index 38 with respect to the scale 39.

In operation, the novel bulb assembly is connected by means of the union parts and clamping rings hereinabove set forth, into the pipe line in which pressures are to be measured. .Upon an increase of fluid pressure within the pipe line, and therefore within the cylindrical element Il), the thin wall I3 of the latter will 'tend to yield, and will be strained in a sense to slightly increase the internal diameter of the tube. The volume of the annular chamber 2l) will thus be reduced; and, as'the thick wall l1 of the element I4 will remain substantially undistorted, some ofthe liquid in the chamber 2i] will be forced out into the capillary tube 22, causing the index 38 to excurse along the scale 39, and provide a measure of the fluidpressure within the bulb. The constri'cted nature of the capillary tube 22 willtend to damp iluctuations in pressure, thus providing a relatively steady reading on the gauge Without the necessity of throttling or otherwise restricted orifices in the flow of the liquid within the pipe line. Moreover, by properly proportioning the dimensions of the capillarytube to those Vof other elements of the device and to the pressures involved, the degree of damping `may be predetermined to a satisfactory degree of accuracy. At the same time, any change ofthe ternperature of the fluid within the bulb or of the ambient atmosphere will affect the two opposed systems in equal .and opposite senses, and will produce no resultant effect on the reading ofthe index 38. Thus, the Bourdon spring -31 may be said to function as a measuring element, whilethe spring 36 functions as a compensating element.

In the alternative form of bulb shown in Fig. 4

'the coaxial arrangement of annular liquid chambers about the axis of the pipe line is maintained; but, instead of one chamber encircling theother as in the embodiment shown in the preceding figures, I nally displaced, thus bringing the thick-walled compensating chamber into intimate thermal association with the fluid under measurement.`

This is accomplished by the use of the following structural embodiment: A tubular elementl 4l having an internal diameter suitable to carry the flow of the fluid under measurement is formed with its walls reduced to two different thicknesses. A portion 42 is turned down to a relai tively thin section, adapted to yield, though not beyond its elastic limit, to the pressures to be measured. A portion 43 is turned down to an extent to provide an annular groove on the outside surface, but leaving a wall of sufficient thick-I ness not to yield appreciably under the pressures encountered. End portions 44 and 45 are left the fulldiameter of the tubular stock, and an interthe chambers are longitudi- A similar tubular element 49 is placed over the reduced portion 43 having its inner end partially overlapping the portion-46 and its outer end `flush with the corresponding end of element 4l, thus forming an annular chamber 50. The inner ends of the tubular elements 41 and 4 9 are sealed to the portion 46 as by brazing in a ring of silver solder 5l, and the outer ends are similarly sealed to the unreduced end portions 44 and 45 of the element 4I.

A capillary tube 52 is passed through the end portion 44 and sealed therein by-brazing, placing its interior bore in communication with the Y chamber 48'; and a capillary tube 53 is similarly passed through the lend portion 45,.placing its interior bore in communication with the chamber.50.`

A massive metallic elongated body partA 54 has formed axially therethrough a cylindrical bore of diameter'equal to the outside diameter of the tubular elements 41 and 49, and is adapted to contain and support the same together with the enclosed .element 4I when concentrically positioned therein. Lateral openings 55 'and 56 near the extremities of said body part provide means for bringing the capillary tubes 52 and 53 to the outside surfacel of same; and the outer portions of said openings are threaded to accommodate plugs or nipples 51 and 58 adapted to guide and protect said capillary tubes and to provide mountings for armor or other protective devices n-ot shown in the drawings. The extremities of the body portion 54 are seated and threaded in the conventional manner to provide convenient connection means to the pipe line in which fluid pressures are to be measured.

The assembly of the tubular elements 41 and 49, with thel enclosed element 4I and attached capillary tubes, is positioned within the body part 54, the capillary tubes lbrought out through the lateral openings, and the whole sealed in position by means of fillets of solder or other material flowed in a liquid or plastic state into place, and allowed to enter the openings 55 and 56, solidifying there and securing 'the capillary tubes therein and retaining the plugs 51 and 58 in place. The fillets. are formed at the'extremities `of the element 4I into smooth flares 59 and 59', presenting n o sharp corners or interstices subject to the accumulation of deposits or difcult to clean when the devicel is disassembled. The whole assembly of the massive body part 54 with its enclosed 'tubular elements permanently attached thereto thus constitutes an annular internal-fluid-pressure-sensitive bulb adapted for all the purposes and applications of the corresponding element hereinabove described and shown in the preceding figures. For purposesl of use, the capillary tube 52, communicating with lthe thin-walled chamber 48, is connected to the 41 having'an internal diam- 5 to the "compensating system of the gauge. Both systems ,are lled with an incompressible fiuid, and sealed. Variations in temperature of uid passing through the tubular element 4| will be communicated to the liquid in both chambers;

. and, these chambers being properly proportioned of the contained liquid through the capillary tube 52 into the measuring element of the gauge, while the relatively thick wall 43 will not yield appreciably, so that no corresponding deection of the compensating element will beproduced, with the result that the measuring instrument or pressure gauge will indicate upon its dial a measure of the pressure within the bulb,

Without respect to temperature of the fluid under measurement or of the surrounding atmosphere.

In Fig. 6 is shown an alternative form which may be given vto the internal thin-walled pressure-sensitive tubular element without departing from the spirit of the invention. The circular tubular element v4| of the fitting shown in Fig. 5 is here replaced by an element 4| having its reduced portion of slightly flattened or elliptical section, such as would be obtained by applying a lateral compressive force before completing the assembly. The element 4I is positioned within the non-deformable tubular element v11 in a manner identical with the element 4I, thus providing a surrounding chamber 48. It will be obvious that internal fluid pressure will tend to increase the sectional area by causing the section to approach a circular form, effecting a corresponding reduction in the section Aarea of the surrounding annular chamber, and

a resultant decrease in its volume.

The chamber 48' being placed in closed communication with a suitable pressure gauge in a manner identical with that herein above set forth, and the system completely filled with liquid, any change in volume will be reflected in a change in the reading oi' the pressure gauge,

being made of dimensions such that it will yield tol uid pressures of the order of those involved in the measurement. The wall portion 61, while reduced to substantially the same thickness as the portion 66, has left thereon a series of ring portions 68 of the original diameter of the tube,

, thus providing mechanically supporting members tially the same thermal conductivity as the walls of chamber 64 but so supported as not to be subject toaappreciable deformation under pressure.

In Fig. 9 is shown a differential manometer clement 7U having a pointer 'Il adapted by its excursion with respect to a graduated scale 12 to provide a measure of difference of two iluid pressures applied to its measuring element through two tubular members 13 and 14. A conduit 15 adapted to carry a fluid whose rate of flow it is desired to measure, hasy placed in its course an oriice plate 16 of the conventional type used for such measurement. On each side vof the orifice plate 16 are connected in the conduit fittings l1 and 18, each of the type hereinbefore disclosed, and adapted to reproduce variations in pressure of the fluid flowing therethrough as variations in pressure in a liquid contained in an auxiliary compartment. of the fittings 'l1 and 'I8 are placed in communication respectively with the tubular members 13 and 14, whereby pressures are imparted to the manometer element 1U, whose indications`will thus become a measure of the rate of flow in the conduit 'l5 and through the orifice plate 16. Ordinarily the transfer of fluid from one to the other of the ttings 11 and 18 `will be suicient to maintain them at substantially the same temperthus providing a measure of uid pressure within the deformable tubular element 4i. While the chamber 48 is shown as having a cylindrical exterior wall, it is obvious that, should such procedure be found desirable, the volume of contained liquid may be materially reduced by making this wall of a section having the form of an ellipse with its axes parallel to the correspondir'ig axes of the'section of element 4i'.

In the form of construction shown in Figs. 7 and 8, there is ,illustrated an alternative form which may be 'assumed Vby the compensating chamber which is the chamber having the nondeformable wall. -A body portion similar in all respects to the body portion 54 shown in Fig. 4, has tightly positioned therein a pair of tubular elements 6| and 82, enclosinga tubular element 63, and forming therewith two annular chambers 64 and 85, each adapted to contain an incompressible fluid, and adapted for communication with the respective sides oi' a dilerential pressure gauge as hereinbei'cre set forth. The reduced wall portions 86 and 61 of the chambers 64 and 65, respectively, are formed by turning the material of the tubular element 63 down to substantiallythe same thickness for each chamber. The wall portion B6 is formed in a manner identical with the portion 42 shown in Fig. 4,

ature; and. with the respective tubular members 13 and 14 enclosed in a common metallic armor 19, they also will bemaintained at a common temperature, so that the temperature compensating device shown as a part of the fitting where direct measurement of pressure is required, will become unnecessary where vsuch measurements as that of ow are involved.

It will be obvious to those versed in the art that while for purposes of simplicity the invention has been shown as having an internal metallic surface directly in contact with the fluid Whose pressure is to be measured, the sensitivity and accuracy of the device will not be adversely affected' by lining the interior surface with a flfexible enamel or by placing therein a thin-walled resilient tube of rubber, neoprene or thelike, to protect the metallic surface .from the action of "corrosive fluids.

ment, yet in certain installations there may`ber mechanical limitations making such an arrangement impracticable. In such instances it is to be understood that without in any way departing from the spirit of the invention the tting may be capped at oneend, thus forming a chamber adapted to contain a portion of the uid whose pressure is to be measured, and placed in com- Said compartments or chambers' 1.v In a devicev for measuring the pressure of a flowing fluid: a fitting including a conduit adapted to the internal passage of said fluid and having an axially extending elastic wall portion of circular cross-sectional contour transversely of the conduit, an enclosed body part surrounding said elastic wall portion to provide a closed chamber of variable volume, the chamber being com,

pletely lled with a fluid subjected to compressive force by deformation of said wall, and fluid-pressure measuring means in communication with said chamber.

2. In a device for. measuring the pressure of a flowing fluid irrespective of temperature, the combination of an extended conduit of circular cross-sectional contour adapted to the internal passage of said fluid, said conduit having axially displaced wall portions-of different characteristics, one being elastic and adapted to yield under the pressure to be measured, and another substantially rigid under said pressure, a rigid tubular member surrounding said conduit and being separated from its said wall portions by annular chambers enclosed thereby, together with a differential pressure gauge communicating respectively wlth said chambers and adapted to respond differentially to changes in pressure therein.

3. In a device for measuring the pressure of a flowing uid irrespective of temperature, the combination of an extended conduit of circular cross-sectional contour adapted to the internal passage of said fluid, said conduit having axially rigid tubular element surrounding said first tu.

a body of said fluid, and a rigid part surrounding said tubular part spaced therefrom and forming thereabout an annular closed chamber coaxial with said tubular part, said yieldingwall portion being common to said space and said chamber, whereby the volume' of said chamber will vary with deformation of said'yieldable wall portion with changes in pressure of said uid, said chamber being lled with a liquid subjected to compressive force varying with said volume variation, and duid-pressure measuring means in communication with said chamber.

6. In adevice for measuring the pressure of a owing fluid irrespective of temperature, the combination of a conduit of circular cross-sectional contour adapted for the internal passage of said fluid and having a wall portion deformable under-pressure of said fluid, a first rigid tubular element surrounding said conduit and spaced therefrom byspacing elements to form a first sealed chamber coaxial therewith, a second l bular element and spaced therefrom by spacing displaced deformable wall portions, one adapted to yield under the pressure to be measured, and another having circular ribs Vto maintain said wall portion substantially rigid under said pres sure, a rigid tubular member surrounding said i conduit and being separated from its said wall portions by annular chambers enclosed thereby,

together with a differential pressure gauge communicating respectively with said chambers and adapted to respond differentially to changes in pressure therein.

4. In a fluid-pressure-measuring device, the combination of a conduit of circular cross-sectional contour adapted to carry a stream of said uid under pressure, said conduit having elastic wall portions, an extended, substantially rigid, tubular element surrounding said conduit and for a portion of its length separated therefrom by an annular sealed chamber, an extended body portion surrounding said tubular member, and for a portion of its length separated therefrom by a second annular sealed chamber concentric with said first-named chamber, means for connecting said body part into a pipe-line carrying said fluid, and a differential pressure gauge having o ppositely-responding pressure-sensitive members communicating respectively with said chambers.

5. In a device for measuring the pressure of a fluid in a conduit: a fitting adapted to be incorporated as a portion of said conduit and including a tubular part having a yielding smooth wall portion defining a space adapted to enclose elements to form a second sealed chamber coaxial therewith, the walls of said conduit and said rst tubular element being thermally conducting, and a'. differential pressure gauge having pressure responsive elements communicating respectively with said chambers.

'7. In a device for measuring the pressure of a fluid in a conduit: a tting adapted to be incorporated as a portion of said conduit and including a tubular part having a yielding smooth thermally-conducting wall portion defining a space adapted to enclose a body of said fluid, and a rigid,part surrounding said tubular part spaced therefrom and forming thereabout an annular closed chamber coaxial with said tubular part, said yielding wall portion being common to said space and said Ichamber, whereby the volume of said chamber will vary with deformation of said yieldable wall portion with changes in pressure of said fluid, a second closed chamber of substantially constant volume interiorly isolated from said rst chamber to be independent of pressure changes therein but in intimate thermal association therewith, said chambers being filled with separate bodies of liquid, the liquid in said firstnamed chamber being subjected through said yielding wall to compressive force Varying with said volume variation, together with a differential pressure gauge communicating respectively with 'said chambers and adapted to respond differentially to pressure lchanges, therein. 8. In a device for measuring the pressure of a owing lluid: a tting including a conduit adapted to the internal passage of said fluid and having an axially extending deformable elastic wall portion of non-circular cross-sectional contour surrounding said fluid, and subject to deformation with changes in the pressure of said fluid, an enclosed body part surrounding said portion and formingv therewith a closed chamber, the chamber being completely filled with a fluid subject to compressive force by the deformation of said wall, and fluid-pressure measuring means in communication with said chamber.

9. In a device for measuring the pressure of a a rigid part surrounding said tubular part spaced therefrom and forming thereabout an annular closed chamber coaxial with said tubular part,

' said yielding wall portion being common to said space and said chamber, whereby the interior of said chamber will be in intimate thermal association with said fluid and the volume of said chamber will vary with deformation of said yieldable wall portion with changes in pressure of said uid, a second closed chamber of substantially constant volume interiorly isolated from said rst chamber to be independent of pressure changes therein and having a thermally conducting wall portion in intimate thermal association with said fluid, said chambers being filled with separate bodies of liquid. the liquid in said rstnamed chamber being subjected through saidyielding wall portion to compressive force varying with said volume variation, and both said bodies of liquid tending through said conducting wall portions to assume the temperature of said y uid, together with a diierential pressure gauge communicating respectively with said chambers 

